Aromatic L-amino acid decarboxylase (AADC) is a homodimeric pyridoxal phosphate-dependent enzyme responsible for the synthesis of dopamine and serotonin. The encoded protein catalyzes the decarboxylation of L-3,4-dihydroxyphenylalanine (L-DOPA or levodopa) to dopamine; L-5-hydroxytryptophan to serotonin; and L-tryptophan to tryptamine. Defects in this gene are the cause of aromatic L-amino-acid decarboxylase deficiency (AADCD), which is an inborn error in neurotransmitter metabolism leading to combined serotonin and catecholamine deficiency that results in severe motor and autonomic dysfunctions.
Parkinson's Disease (PD) is a progressive neurodegenerative disease of the central nervous system (CNS) producing sensory and motor symptoms. Dopamine replacement (i.e., levodopa) has been the standard pharmacotherapy for motor impairment in PD. However, the benefit of dopamine therapy becomes less marked over time, due, in part, to the progressive death of dopamine-generating cells and corresponding loss of AADC activity. Furthermore, systemic administration of high-dose dopamine is complicated by side effects, such as fluctuations in motor performance, dyskinesias, and hallucinations, resulting from dopaminergic stimulation of the mesolimbic system. One strategy to restore dopaminergic function and minimize side effects is the use of gene therapy to deliver AADC directly to a targeted region of the CNS.
The adeno-associated virus (AAV) has emerged as an attractive vector for gene therapy due to its long-term gene expression, the inability to autonomously replicate without a helper virus, the ability to transduce dividing and non-diving cells, and the lack of pathogenicity from wild-type infections (See e.g., Hadaczek et al. Mol. Ther. 18(8), 1458-1461, August 2010). AAV is a helper-dependent DNA parvovirus which belongs to the genus Dependovirus. 
The present invention provides such improved nucleic acid constructs, e.g., polynucleotides, for use with AAV-derived vectors comprising dopa carboxylase (“DDC”) gene sequence which encodes a full-length AADC protein for the purpose of gene therapy in the treatment of Parkinson's Disease.
The nucleic acid constructs described herein comprise at least a 5′-ITR and a 3′-ITR, each or both of which may be derived from an AAV, positioned about a DDC gene sequence, as well as additional components required for gene expression and clone selection.